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^<^'X ;(^**DProceediii8S 23d Annual Meeting 

^SOCIETY FOR PROMOTION 

AGRICULTURAL SCIENCE 



THe Available Energy 

of TimotHy Hay 



By HENRY PRENTISS ARMSBY, PH. D., 



and 



J. AUGUST FRIES, 



State College, Pennsylvania. 



7/ 



»«■■■« 



^ »i» 1902 1? ^ 






ll^e ^Available Energy of Timoil^y Hay. 



By Henry Prentiss Armsby, Ph., J)., and J. August Fries, 
State College, Pennsylvania. 

The increasing interest and importance attaching to 
the study of the nutrition of domestic animals, as well as 
of man, from the standpoint of the energy involved in- 
duced the Pennsylvania Experiment Station to undertake 
the construction of a respiration-calorimeter upon the 
pi in devised by Atwater & Rosa, bnt enlarged and modi- 
fied to admit of experiments upon cattle. In the con- 
struction and operation of this expensive apparatus, 
the Station has enjoyed the cooperation of the Bureau 
of Animal Industry of the U. S. . Department of Ag- 
riculture, and with the permission of its Chief, Dr. D. 
E. Salmon, the following preliminary report of some 
of the results is presented. Acknowlegment should also 
be made of the skill and faithfulness of our assistants, 
Messrs. C. W. Norris, J. B. Robb, T. M. Carpenter and N. 
W. Buckhout, in the execution of the laborious respira- 
tion and calorimetric experiments and of the coopera- 
tion of the Chemical Division of the Station, under the 
direction of Dr. Wm. Frear, in the examination of feeds 
and excreta. Dr. C. A. Browne, Jr., having had general 
charge of the reception and care of samples and having 
executed the determinations of carbon and hydrogen, 
while the determinations of heats of combustion have 
been made by Mr. Norris. 

The experiment constitutes a study of the energy-con- 
tent of timothy hay (this material having been selected 
because it constitutes a fairly definite farm product) and 



THE AVAII,ABI<E ENERGY OF TIMOTHY HAY. 97 

oi the use made of this energy in the organism of cattle. 
Although few in number, the results seem to us worthy of 
consideration in the light of suggestions for further inves- 
tigation, while they possess a certain interest also as being, 
so far as we are aware, the first direct determininations 
of the heat production of a farm animal. 

At the outset, one or two definitions seem desirable. 
The heat of combustion of a material like timothy hay 
measures the total amount of kinetic energy which we can 
obtain from it. This quanity is commonly spoken of as the 
potential energy or "gross energy" of the hay. By no 
means all of this gross energy is capable ,of being used by 
the animal organism. A considerable proportion of it re- 
appears as potential energy in the various excreta, solid, 
liquid and gaseous, of the animal, and therefore escapes 
from the body entirely unused for its purposes. By sub- 
tracting the quantity of potential energy thus rejected by 
the body from the total amount supplied in the food we 
obtain the amount which is capable of conversion into 
the kinetic form in the organism. This portion has been 
somewhat commonly designated as "available" energy, 
or more specifically as "gross available" energy to indi- 
cate that it represents the maximum amount available 
for any purpose. We shall see presently, however, that 
there are not wanting indications that a portion of this 
so-called available energy may in some instances be of no 
direct use to the organism; that is, that it may neither serve 
immediately to maintain the vital processes nor add to the 
store of potential energy in the body, but simply increase 
the heat production of the animal. We therefore venture 
to propose the substitution for the term available energy, 
oftheterm. metuboliziible energy as equivalent to energy of 
food minus energy of excreta. Although not particularly 
euphonious, this term has the advantage of expressing 
the facts of the case, while avoiding any implications re- 
garding the uses to which this energy is put in the body, 
as well as the necessity of using the word available in t\Yo 
senses. 

Rubner's well-known experiments^ with dogs and 



'Zeit. f. Biol., 19, 312. 



98 THE AVAILABLE ENERGY OF TIMOTHY HAY. 

other animals showed that, at or below the maintenance 
requirement, nearly pure nutrients could be substituted 
4n the metabolism of the animal for the ingredients of 
body tissue, and that they were valuable for this purpose 
approximately in proportion to their metabolizable energy 
as above defined. For example, Rubner found that when 
neark pure proteids were given to a fasting dog, the 
amount of proteids destroyed in the body was largely 
increased, but that a correspondingly smaller amount of 
fat was oxidized, and further that the proteids replaced 
fat in inverse proportion to their content of metabolizable 
energy. Under these conditions there was, of course, no 
increase in the total amount of heat produced in the body 
but simply a substitution of one kind of fuel for another. 
Rubner experimented with fats and carbohydrates as 
well as with proteids and found the same law to hold, 
while in a single experiment he also substituted carbo- 
hydrates for fats in the food in a corresponding ratio. 
This law of the substitution of nutrients in the manner 
just indicated is called by Rubner the law of isodynamic 
replacement and the relative values of the nutrients as 
deduced from it, isodynamic values. Rubner experiment- 
ed chiefly with carnivora, but his law has been generally 
assumed to apply to all animals. Thus Kellner^, in his 
extensive investigations upon cattle, regards the results 
which he obtained for the metabolizable energy of various 
materials as representing their value as part of the 
maintenance ration and speaks of them as replacement 
Yalues (Vertretungswerte). 

It has been well established by the investigations of 
Zuntz and others that there is a not inconsiderable ex- 
penditure of energy in the digestion and assimilation of 
the food. This energy must ultimately assume the form 
of heat in the body, the amount of heat produced depend- 
ing on the kind and amount of food consumed. This 
would seem to imply an increase in the heat production 
with increasing quantities of food, and therefore 
to contradict the law of isodynamic replacement. 
Rubner explains this apparent discrepancy by the 



^ Landw. Vers. Stat., 53, 440. 



THE AVAILABLE ENERGY OF TIMOTHY HAY. 99 

hypothesis that the heat into which the energy expended 
in digestion and assimilation is ultimately converted is 
substituted in the body for an equivalent amount of heat 
which would otherwise be produced by oxidation of body 
substance, so that there is no increase in the total heat 
production. 

Kubner's conclusions have exerted a profound influence 
upon the science of nutrition, but at the same time their 
value lies more largely in the point of view which they 
opened up than in their exact numerical accuracy. As 
just stated, isodynamic replacement implies that there is 
no increase in heat production with an increasing amount 
of food. As a matter of fact, however, the great majority 
of Rubner's experiments do show more or less increase in 
the heat production, the only exceptions being a single ex- 
periment with fat, and three or four upon cane sugar, 
some of which Rubner himself considers of doubtful value. 
From theoretical considerations the writer has been led 
to question the entire applicability of Rubner's law to 
herbivorous animals, and especially to ruminants with 
their large expenditure of energy in digestive work, and 
the experiment here reported was planned to test the 
equivalence of the metabolizable energy of hay and that 
of body tissue. 

Four different amounts of timothy hay, with the ad- 
dition of a small uniform amount (400 grms.) of linseed 
meal, were fed to the same steer, weighing about 400 
Kgs. Each ration was fed for two weeks, during the second 
of which the visible excreta were collected quantitatively 
and during which the animal passed 48 hours in the 
respiration-calorimeter at the uniform temperature of 
18.2° C. for the determination of gaseous excreta and heat 
production. 

Passing over the details of the experiments, only the 
final results as regards energy are presented here, as fol- 
lows: — 



roo 



tHK AVAIXABI.E ENERGY OTF TIMOTHY HAY". 



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Comparing the four periods, we note at once that with 
increasing amounts of feed the heat production also 
shows a material increase, which should not be the case if 
isodynamic replacement took place in accordance with 
Rubner's theory. 

Proceeding now to consider the results quantitatively, 
we may for simplicity set aside the energy of the excreta 
and compare directly the amount of metabolizable energy 



103 

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12000 Cals. l:MOO Cals. 
rZABLE ENERGY. 





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"THE AVAII^ABLE ENERGY OF TIMOTHY HAY. 



103 



furnished the animal in each period with the nutritive 
effect produced. This effect is measured by the extent to 
which loss of tissue was prevented below the maintenance 
ration, or by the increased gain above maintenance, and 
may be compared in the different periods by re^^arding the 
ration of Period A as a basal ration and subtracting the 
results for that period from those of the other three. 

Thus, comparing- Periods A and B, we find that in 
Period B 2864 Cals. of metabolizable energy were added 
to the basal ration and diminished the loss of tissue by 
1725 Cals., or in other words that 60.24 percent, of the 
additional metabolizable energy supplied was used for 
maintenance, while 39.76 per cent, gave rise to the pro- 
duction of heat which was in excess of the needs of the 
animal, so far as maintaining the body temperature was 
concerned, since the normal temperature was maintained 
on the lesser supply of metabolizable energy. 

The results of similar comparisons for each of the 
three periods are contained in the following table, and are 
also represented graphically by the full Hue in the accom- 
panying diagram, in wnich the abscissae represent the 
quantities of metabolizable energy supplied to the animal 
^-i^and the ordinates the resulting gain or loss of energy by 
the body. The points show the results for each period 
and the line the average result: 





Metabolizable 
Energy. 
Cals. 


Gain of 

Tissue. 

Cals. 


Gain in 

per cent, of 

Metabolizable 


Period B 

" A 


9482 
6618 


— 724 
-2449 




Difference 


2864 


1725 


60.24 


Period C 
" A 


11222 
6618 


+ 616 
-2449 




Difference 


4604 


3065 


66.57 


Period D 

" A 


12255 

6618 


-fl072 
—2449 




Difference 


5637 


3521 


62.46 


Average 






63.09 



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7000 Cnls SOOO Hals 9000 Cala. 10008 Gala. 11000 Cala. 12000 CalH 1:1000 Cala 

metabolizabIjE energy. 



iq4 THE AVAItABI^E ENERGY OF TIMOTHY HAY. 

It is obvious that in each case a considerable propor- 
tion of the inetabolizable energy of the added food was 
used for other purposes than the maintenance of body 
tissue, the amount thus expended ranging, in round num- 
bers, from 33% to 40%, and averaging 37%. In other 
words, the metabolizable energy of the hay had only 
about 63% of the nutritive value which the theory of iso- 
dynamic replacement would ascribe to it. The same fact 
is, of course, indicated in the graphic representation by 
the fact that the line representing the average results 
make an angle of more than 45 degrees with the vertical. 

The facts that the external conditions, particularly 
temperature and relative humidity, were almost absolute- 
ly identical in the four periods, and that the smallest 
amount >:f heat produced was sufficient to prevent any 
material fall of body temperature for two weeks, seem . to 
negative the supposition that the additional heat evolved 
in the later periods was a mere production of heat for its 
own sake. 

There was no noticeable difference in the several 
periods as regards the muscular activity of the animal, 
with the exception of differences in the amount of time 
passed respectivnly in the standing and lying posture.^ 
This difference, however, was not inconsiderable, the 
number of minutes per 24 hours passed in the standing 
position ranging, during the eight days of the respiration 
trials, from 675 to 1026. The muscular exertion neces- 
sary to maintain the standing posture is an important 
source of heat. In this experiment the amount of heat 
given off from the animal by radiation and conduction 
and brought out of the calorimeter in the water current 
has been computed separately for the periods when the 
animal was standing or lying, omitting from the compu- 
tation all periods of less than three hours. The ratio of 
heat given off while lying to that given off while standing 
was as follows: 



Period A 1 

Period B 1 

Period C 1 

Period D 1 



1.321 
1.332 
1.296 
1,286 



We have no means of comparing in a similar way the 



THE AVAILABIvK ENERGY OF TIMOTHY HAY. 



105 



heat given off by the animal as latent heat of water 
vapor. If, however, we make the not improbable assump- 
tion that this amount was proportional to that given 
off by radiation and conduction, we may computf> the 
total amount of heat produced respectively in the lying 
and the standing position per minute or per 24 hours 
with the following results: 



Period A 
B 

" C 
D 



Heat Production (per 24 hours) 



Observed. 
Cals. 



9067 
10206 
10606 
11183 



Computed 
Lying. 
Cals. 



7664 
8325 
9086 
9512 



Computed 
Standing. 
Cals. 



10125 
11088 
11772 
12232 



Comparing these computed amounts ot heat, we can 
also compute the gain or loss of tissue and its relation to 
the metabolizable energy supplied, in the same manner as 
before, with the results contained in the following tables 
and represented by the broken lines in the diagram: 



I 





Metabolizable 

Energy. 

Cal. 


Gain, 

Lying. 

Cal. 


Gain in 

per cent, of 

Metabolizable 


Period B 
A 
Difference 

Period C 
" A 
Difference 

Period D 
" A 
Difference 
Average 


9482 
6618 
2864 

11222 
6618 
4604 

12255 
6618 
5637 


+1157 

-1046 

2203 

+2136 

-1046 

3182 

+2743 

-1046 

3789 


76.92 
69.12 

67.22 
71.09 



io6 



THE AVAILABLE ENERGY OF TIMOTHY HAY. 





Metabolizable 

Energy. 

Cal. 


Grain, 

Standing. 

Cal. 


Gain in 

per cent, of 

Metabolizable 


Period B 
A 

Difference 


9482 
6618 
2864 


—1606 

-3507 

1901 


66.51 


Period C 
A 
Difference 


11222 
6618 
4604 


- 550 

-8511 

2961 


63.31 


Period D 
A 
Difference 
Average 


12255 
6618 
5637 


+ 23 

—3511 

3534 


62.70 
64.51 



According to these figures, if our animal had passed 
all his time in the recumbent posture he would have 
gained upon each ration except the first one, while, on the 
other hand, if he had spent all his time standing, he would 
have lost upon everj ration except the heaviest. It is 
scarcely necessary to do more than call attention to 
the practical importance attaching to this large difference 
between the metabolism of the animal in the two posi- 
tions. Its bearing upon the differences observed in the 
productive power of different animals, as well as 
upon questions of practical management, is obvious. 

But while the absolute results thus computed differ 
materially from each other and from those actually ob- 
served, the elimination in this way of the influence of 
varying amounts of muscular exertion does not material- 
ly affect the main result. There is still a large percentage 
of the metabolizable energy which is not used for con- 
structive purposes, although the proportion appears to 
be somewhat less when lying than when standing. The 
most natural supposition is that this energy is expended 
in the digestion and assimilation of the food. Apparent- 
ly the amount of heat thus produced, even on the loweist 
ration, was so large a? to reach or pass the limit of 
possible substitution for heat which would otherwise be 
produced by the oxidation of tissue. As food was added 



THE AVAII.ABLE ENERGY OF TIMOTHY HAY. 107 

above this amount, tlie heat resulting from its digestion 
and assimilation was necessarily in excess of the needs of 
the organism under the conditions of the experiment and 
became simply an excretum. 

If this interpretation of the results is correct, it has 
important theoretical bearings. It becomes evident, in 
the first place, that the maintenance requirement of cattle 
is a question of tissue replacement rather than of heat 
production, and, therefore, that the ^alue of a given feed- 
ing stuff for maintenance depends upon the availability of 
its energy. We may, for instance, regard it as at least 
very probable that the work of digestion and assimilation 
in the case of a material like corn meal would be material- 
ly less than in the case of hay; or, in other words, that a 
larger percentage of its energy would be availab e for the 
maintenance of tissue. It would follow from this that in 
case of a ration consisting largely of grain a less amount 
of material or of metabolizable energy would be required 
for maintenance than in the case of a ration consisting 
exclusively of coarse fodder. In other words, the main- 
tenance raticm is a variable rather than a constant, de- 
pending upon the kind of food used. It may be noted 
that this conclusion has already been indicated by the 
experiments upon the maintenance ration of cattle made 
at this Station in 1896-7.^ 

Furthermore, if the heat production upon the 
maintenance ration is in excess of the requirements of 
the animal, it seems unlikely that small variations in 
the stable temperature to which the animal is exposed 
will have the effect upon the maintenance requirement 
which is ordinarily attributed to them. Still less is this 
likely to be the case with fattening cattle, where the 
amount of food and the consequent heat production are 
largely in excess of the maintenance ration. 

Another important point indicated by our results is 
that the availability of the metabolizable energy of the 
food for tissue building is approximately constant within 
the range of the experiment, or, in other words, that the 
gain is a linear function of the amount of metabolizable 

^Bulletin 42, p 159. 



Io8 THE AVAILABLE ENERGY OF TIMOTHY HAY. 

energy supplied. While this is not exactly true, the varia- 
tions from it, as shown by thedingrara, are comparatively 
small, and probably within the limits of experimental 
error. We should anticipate that the inuscala.r work of 
digestion would be approximately proportional to the 
total diy matter supplied. As the figures show, the pro- 
portion of the total energy of the hay which was found to 
be metabolizable diminished as the amount was increased, 
the difference arising chiefly from differences in digestibil- 
ity. Since, nevei'lheless, the total expenditure of energy 
indigestion and assimilation appearstobe approximately 
proportional to the metabolizable energy, it seems 
evident that a large share of this expenditure must be for 
the work of assimilation. Probably a very large factor 
in it is the loss of energy in the methane fermentation. 

Still another indication afforded by our results is that 
the availibility of the metabolizable energy w^as stibstant- 
ially the same above and below the maintenance require- 
ment. This is indicated both by a comparison of the 
actual results in Periods C and D, dnd also b'-^ a compari- 
son of the computed results lying and standing. We 
might anticipate that the conversion of the as-imilated 
food into tissue would require a still further expenditure 
of energy, and that consequently the availability above 
the maintenance requirement would be less than that 
below it. Our experiments, as noted, afford no clear 
indication of such a difference; indeed the availability 
above the maintenance requirement, as computed from 
from the results while lying down, is greater than that 
below the maintenance requirement as computed from the 
results while standing, In view, however, of the 
assumptions involved in the computation, too much 
weight should not be laid upon this point, and we present 
it rather as a suggestion for future research than as a 
eonclusion. It may be noted also in this connection that 
Kellner's experiments in which meadow hay was added to 
a basal ration showed a utilization of the metabolizable 
energy for fattening of less than 42 per cent, as compared 
with the 63 per cent, of availability found in our experi- 
ments. 

The results of our work, then, may be briefly sum- 



THE AVAII,ABr<E ENERGY OF TIMOTHY HAY. IO9 

marized as follows, it being understood that they are 
presented tentatively, and that they apply primarily to 
the conditions of this experiment, namely, a rather high 
stall temperature and comparatively light rations con- 
sisting chiefly of coarse fodder: 

1. The nutritive value of timothy hay, either for 
maintenance or production, was not measured by its 
metabolizable energy, but was in every case materially 
less. In other words the digestible nutrients of the hay 
did not replace body tissue in isodynamic proportions. 

2. The work of digestion and assimilation in the case 
of timothy hay appears to be so great that at, or even 
below, the maintenance requirement, the heat production 
of the animal is in excess of the amount needed for the 
maintenance of body temperature. 

3. The availability of the metabolizable energy of 
timothy hay, within the range of these experiments, ap- 
pears to be a linear function of its amount. 

4. The experiments afford no clear indication that 
the availability is less above than below the maintenance 
requirement. 



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